Method for preparing a composition comprising perfluoropolyether having a carboxyl group at one terminal

ABSTRACT

An object of the present invention is to provide a method for efficiently and highly selectively preparing a composition comprising a perfluoropolyether having a carboxyl group at one terminal at a higher ratio. The present invention provides a method for increasing a ratio of a perfluoropolyether having a carboxyl group at one terminal, relative to a total amount of the perfluoropolyether having a carboxyl group at one terminal and a perfluoropolyether having carboxyl groups at both terminals in a composition comprising these perfluoropolyethers, wherein the method comprises a step of subjecting the composition to chromatography in which a moving phase is supercritical or subcritical state carbon dioxide of the specific temperature and the specific pressure, and a stationary phase is silica gel to thereby collect a fraction containing the perfluoropolyether having a carboxyl group at one terminal at a higher ratio. Further, present invention provides for increasing a ratio of a perfluoropolyether having a carboxyl group at one terminal, relative to a total amount of the perfluoropolyether having a carboxyl group at one terminal, a perfluoropolyether having carboxyl groups at both terminals and a perfluoropolyether having no carboxyl group at any terminal perfluoropolyether, in a composition comprising these perfluoropolyethers, wherein the method comprises a step of subjecting the composition to chromatography in which a moving phase is supercritical or subcritical state carbon dioxide of the specific temperature and the specific pressure, and a stationary phase is silica gel to thereby collect a fraction containing the perfluoropolyether having a carboxyl group at one terminal at a higher ratio.

CROSS REFERENCE

This application claims the benefits of Japanese Patent application Nos.2014-021355 filed on Feb. 6, 2014 and 2014-089380 filed on Apr. 23,2014, the contents of which are hereby incorporated by reference.

FIELD OF THE INVENTION

The present invention relates to a method for preparing a compositioncomprising a perfluoropolyether having a carboxyl group at one terminalat a higher ratio.

BACKGROUND OF THE INVENTION

Perfluoropolyethers having a functional group at one terminal,hereinafter referred to as “one-terminal functional derivative”, andperfluoropolyethers having functional groups at both terminals,hereinafter referred to as “both-terminal functional derivative”,hereinafter collectively referred to as “functionalized polymer”, aregenerally used as a precursor of various derivatives for surfactants andsurface treatment agents. For instance, examples of a precursor ofsurfactants which are useful for polymerization include acrylderivatives, amine derivatives and isocyanate derivatives of thefunctionalized polymer. Further, alkoxy derivatives, chlorinederivatives and silazane derivatives of the functionalized polymer areused as a precursor of surface treatment agents.

Properties of the one-terminal functional derivatives are different fromthat of the both-terminal functional derivatives. For instance, theboth-terminal functional derivatives cause extension of a chain orgelation, but the one-terminal functional derivatives do not cause suchactions. Further, a composition comprising a polymer having nofunctional group at any terminal, referred to as “non-functionalizedpolymer”, has a problem such that the composition is not sufficientlycured. Accordingly, it is industrially important to increase a contentof the functionalized polymer in a composition. In the presentspecification, “functional” or “functionalized” means “having a reactivefunctional group” and “non-functionalized” means “having no reactivefunctional group”.

The preparation of a perfluoropolyether having the structure,—(OCF₂)_(p)(OCF₂CF₂)_(q)(OCF₂CF₂CF₂)_(r)(OCF₂CF₂CF₂CF₂)_(s)—, in a mainchain and a functional group at one terminal is difficult. In theaforesaid structure, p and q are, independently of each other, aninteger of from 5 to 300, r and s are, independently of each other, aninteger of from 0 to 80, and a total of p, q, r and s is 10 to 500.Japanese National Phase Publication No. 2009-532432, Patent literature1, describes that the preparation of a composition comprising aone-terminal functionalized perfluoropolyether in the specific content,comprising steps of preparing a mixture of a one-terminal functionalizedperfluoropolyether, a both-terminal functionalized perfluoropolyetherand a non-functionalized perfluoropolyether by fluorinating a part offunctional groups of a both-terminal functionalized perfluoropolyetherand, then, subjecting the mixture to distillation. However, in themethod described in Patent literature 1, the separation is caused bymaking use of difference of boiling points of the components, so thatthe method cannot be used when the molecular weight distribution of atleast one of perfluoropolyethers is wide. The upper limit of themolecular weight is such that the perfluoropolyether can be distributed.The upper limit of the average molecular weight in the Examplesdescribed in Patent literature 1 is approximately 1,000. Therefore, itis difficult to apply the method to a perfluoropolyether having a largermolecular weight.

The preparation of a composition comprising a one-terminalfunctionalized perfluoropolyether in a higher content without anylimitation on a molecular weight and a molecular weight distribution isuseful for preparing materials such as surface treatment agents,lubricants, and elastomers. Therefore, development of a method forpreparing a composition comprising a one-terminal functionalizedperfluoropolyether in a higher content is desired.

Japanese Patent Application Laid-Open No. 2012-233157, Patent literature2, and Japanese Patent Application Laid-Open No. 2012-72272, Patentliterature 3, describe a method such that a mixture of a one-terminalfunctionalized polymer, a both-terminal functionalized polymer and anon-functionalized polymer, in which the content of the one-terminalfunctionalized polymer is large, is prepared by fluorinating a part offunctional groups of a both-terminal functionalized polymer and, then, anon-functionalized polymer is removed. Patent literatures 2 and 3 statethat in the step of fluorinating a part of functional group, thefluorination can be controlled by adjusting the amount of the fedfluorine gas to thereby decrease an amount of the remainingboth-terminal functionalized polymer, so that, a composition comprisinga one-terminal functionalized polymer in a large amount can be prepared.However, a lot of non-functionalized polymers are also formed in thismethod. Patent literatures 2 and 3 also describe removal of thenon-functionalized polymers by adsorption with an ion-exchange resin orthin-film distillation.

Japanese Patent Application Laid-Open No. 2001-164279, Patent literature4, describes a method for the preparation of a fluorinated lubricantused in magnetic recording media, wherein a fluorinated lubricant withan introduced functional groups, such as a piperonyl group, at the bothterminals is subjected to chromatography in which a moving phase issupercritical state carbon dioxide and a stationary phase is silica gelto collect plural fractions and, then, a fraction having large amountsof a functional group is selected to thereby obtain the fluorinatedlubricant having large amounts of a functional group, in particular, 95%or more, based on a total amount of terminal groups. Patent literature 4states that the percentage of the terminal modification of theboth-terminal functionalized polymer is increased from approximately 90%to 99% according to the method.

PRIOR LITERATURES

Patent literature 1: Japanese National Phase Publication No. 2009-532432

Patent literature 2: Japanese Patent Application Laid-Open No.2012-233157

Patent literature 3: Japanese Patent Application Laid-Open No.2012-72272

Patent literature 4: Japanese Patent Application Laid-Open No.2001-164279

SUMMARY OF THE INVENTION Problems to be Solved by the Invention

However, the adsorption process with an ion-exchange resin described inPatent literatures 2 and 3 needs an ion-exchange resin approximatelytwice and a fluorine solvent nine times as much as the polymer, andfurther needs hydrochloric acid. Therefore, this method is unsuitable tomass production and suffers from a bad manufacturing efficiency.Further, the fluorine solvent is expensive and has a high risk onworkers and the environment. Further, it is sometimes difficult toremove ions and organic substances eluted from the ion-exchange resin.In a thin-film, separation occurs on account of difference of boilingpoints and, therefore, efficiency of the separation is bad. Inparticular, when the polymer has a larger molecular weight, thedeference of boiling points on account of the presence or absence of thefunctional group is less, so that the separation is more difficult.Accordingly, properties of a product are poorer.

The method described in Patent literature 4 is suitable to remove anon-functional perfluoropolyether so as to prepare a compositioncomprising a both-terminal functionalized polymer in a higher content.However, it is difficult to selectively and efficiently obtain acomposition comprising a one-terminal functionalized polymer in a highercontent.

An object of the present invention is to provide a method forefficiently and highly selectively preparing a composition comprising aperfluoropolyether having a carboxyl group at one terminal at a higherratio.

Means to Solve the Problems

Carbon dioxide has a critical temperature of 31.1 degrees C. and acritical pressure of 7 MPa and, therefore, becomes supercritical atmilder conditions, compared to other materials, so that it is easierhandle. A density of a supercritical fluid changes depending on atemperature and a pressure. Therefore, it is possible to control itssolute dissolution property so as to dissolve perfluoropolyethers. Thesolubility of perfluoropolyethers in supercritical state carbon dioxidedepends on types of functional groups and the presence or absence of afunctional group. Further, the solubility depends on the molecularweight. A compound having a smaller molecular weight tends to solve inmilder conditions. Therefore, it is very difficult to separate polymershaving a large molecular weight distribution by types of functionalgroups or presence or absence of the functional group in supercriticalextraction. It is necessary to make a molecular weight distributionsmaller in advance.

Now, the present inventors have found a process where terminalfunctionalized groups of perfluoropolyethers is converted into acarboxyl group in advance and a composition comprising theseperfluoropolyethers is subjected to chromatography in which a movingphase is supercritical or subcritical state carbon dioxide of thespecific temperature and the specific pressure and a stationary phase issilica gel to thereby separate perfluoropolyethers efficiently by thepresence or absence of the carboxyl group, so that a fraction containingthe perfluoropolyether having a carboxyl group at one terminal at ahigher ratio is easily obtained.

Thus, the present invention provides a method for increasing a ratio ofa perfluoropolyether having a carboxyl group at one terminal, relativeto a total amount of the perfluoropolyether having a carboxyl group atone terminal and a perfluoropolyether having carboxyl groups at bothterminals in a composition comprising these perfluoropolyethers, whereinthe method comprises a step of subjecting the composition tochromatography in which a moving phase is a supercritical or subcriticalstate carbon dioxide and a stationary phase is silica gel, and themoving phase is at a constant temperature, T, in a range of from 25degrees C. to 150 degrees C. and a constant pressure, P, in a range offrom 7 MPa to 30 MPa to thereby collect a fraction containing theperfluoropolyether having a carboxyl group at one terminal at a higherratio, hereinafter referred to as the first method.

Further, the present invention provides a method for increasing a ratioof a perfluoropolyether having a carboxyl group at one terminal,relative to a total amount of the perfluoropolyether having a carboxylgroup at one terminal, a perfluoropolyether having carboxyl groups atboth terminals and a perfluoropolyether having no carboxyl group at anyterminal, hereinafter referred to as a non-functionalizedperfluoropolyether, in a composition comprising theseperfluoropolyethers, wherein the method comprises a step of subjectingthe composition to chromatography in which a moving phase is asupercritical or subcritical state carbon dioxide and a stationary phaseis silica gel and the chromatography comprises the following step (i′)or (ii′):

(i′) the moving phase is at a constant temperature, T₀, of 25 degrees C.or higher to 150 degrees C. or lower and a constant pressure, P₁, of 7MPa or higher to lower than 30 MPa to thereby collect a fractioncontaining the non-functionalized perfluoropolyether at a higher ratioand, subsequently, the pressure of the moving phase is increased to aconstant temperature, P₂, which is higher than 7 MPa to 30 MPa or lowerand is higher than the aforesaid pressure P₁ to thereby collect afraction containing the perfluoropolyether having a carboxyl group atone terminal at a higher ratio;

(ii′) the moving phase is at a constant temperature, T₁, of higher than25 degrees C. to 150 degrees C. or lower and a constant pressure, P₀, of7 MPa or higher to 30 MPa or lower to thereby collect a fractioncontaining the non-functionalized perfluoropolyether at a higher ratioand, subsequently, the temperature of the moving phase is decreased to aconstant temperature, T₂, which is 25 degrees C. or higher to lower than150 degrees C. and is lower than the aforesaid temperature T₁ to therebycollect a fraction containing the perfluoropolyether having a carboxylgroup at one terminal at a higher ratio, hereinafter referred to as thesecond method.

Effects of the Invention

According to the present methods, a composition comprising theperfluoropolyether having a carboxyl group at one terminal at a higherratio is efficiently obtained. In the present method, a limitation of amolecular weight is small, so that the method can be applied to aperfluoropolyether having a wide molecular weight distribution. Further,the present method decreases an amount of fluorine solvent used, so thatinfluence to environmental burden is small and is suitable to a massproduction.

BEST MODE OF THE INVENTION

The present invention will be described below in detail.

The first invention is a method for purifying a composition comprisingthe perfluoropolyether having a carboxyl group at one terminal and theperfluoropolyether having carboxyl groups at both terminals. This methodis characterized by the step of subjecting the composition tochromatography in which a moving phase is a supercritical or subcriticalstate carbon dioxide and a stationary phase is silica gel, hereinafterreferred to as “a supercritical chromatography”, and the moving phase isat a constant temperature, T, in a range of from 25 degrees C. to 150degrees C., preferably at higher than 25 degrees C. to lower than 150degrees C., and a constant pressure, P, in a range of from 7 MPa to 30MPa, preferably at higher than 7 MPa to lower than 30 MPa, to therebycollect a fraction containing the perfluoropolyether having a carboxylgroup at one terminal at a higher ratio.

In the first method, the aforesaid chromatography may further comprisethe following step (i) or (ii) after collecting the fraction in theaforesaid process.

(i) The pressure of the moving phase is increased to a constantpressure, P′, which is higher than 7 MPa to 35 MPa or lower and ishigher than the aforesaid pressure P to thereby collect a fractioncontaining the perfluoropolyether having carboxyl groups at bothterminals at a higher ratio. In this step, the temperature of the movingphase remains at the aforesaid temperature T. The temperature mayslightly change.

(ii) The temperature of the moving phase is decreased to a constanttemperature, T′, which is 25 degrees C. or higher to lower than 100degrees C. and is lower than the aforesaid temperature T to therebycollect a fraction containing the perfluoropolyether having carboxylgroups at both terminals at a higher ratio. In this step, the pressureof the moving phase remains at the aforesaid pressure P. The pressuremay slightly change.

According to the aforesaid step (i) or (ii), a fraction containing alarge amount of the perfluoropolyether having carboxyl groups at bothterminals can be collected.

According to the aforesaid process, a fraction containing theperfluoropolyether having a carboxyl group at one terminal at a higherratio is collected. That is, the content of the perfluoropolyetherhaving a carboxyl group at one terminal in the composition increases.The aforesaid higher ratio means that the composition comprises theperfluoropolyether having a carboxyl group at one terminal preferably at80 mole % or more, more preferably 90 mole % or more, further preferably95 mole % or more, relative to a total mole of the perfluoropolyetherhaving a carboxyl group at one terminal and the perfluoropolyetherhaving carboxyl groups at both terminals. In the present invention, thepressure of the moving phase means the pressure of the moving phase in ahigh pressure vessel and the temperature of the moving phase means thetemperature of the moving phase in a high pressure vessel.

The carbon dioxide used as a moving phase is in a supercritical orsubcritical state. Carbon dioxide has the critical temperature of 31.1degrees C. and the critical pressure of 7 MPa. In the present invention,the carbon dioxide may be in a subcritical state and not is limited tobe in a supercritical state. The pressure of the carbon dioxide in thepresent invention is in the range of from 7 MPa to 35 MPa, preferably inthe range of from 8 MPa to 30 MPa. The temperature of the carbon dioxideis in the range of from 25 degrees C. to 150 degrees C., preferably inthe range of from 30 degrees C. to 100 degrees C. The flow rate of themoving phase may be properly selected and not limited to any particularone. In a case where a volume of an extraction vessel used is large, alarge flow rate is preferred. The volume of the extraction vessel may beproperly selected, depending on an amount of the composition to bepurified.

In the process comprising the aforesaid step (i), the temperature of themoving phase is preferably fixed. When the temperature is fixed, thesolubility of the compound having a functional group in the moving phaseis higher with a higher pressure of the moving phase. The pressures ofthe moving phase, P and P′, are set, depending on the molecular weightof the polymer contained in the composition and the extractiontemperature T. For instance, when the polymer contained in thecomposition has a weight average molecular weight of 1,000 to 15,000,the extraction temperature T may be in the range of from 25 degrees C.to 150 degrees C., preferably in the range of from 30 degrees C. to 80degrees C., and the pressure P is a constant pressure of 7 MPa or moreto 30 MPa or less, preferably more than 7 MPa to less than 30 MPa,further preferably 8 MPa or more to 25 MPa or less, and the pressure P′is a constant pressure of 8 MPa or more to 35 MPa or less, preferably 10MPa or more to 30 MPa or less, further preferably 15 MPa or more to 30MPa or less, provided that the pressure P′ is higher than the pressureP. In this process, the pressure may be changed in stages between thepressure P and P′.

In the process comprising the aforesaid step (ii), the pressure of themoving phase is preferably fixed. When the pressure is fixed, thesolubility of the compound having a functional group in the moving phaseis higher with a lower temperature of the moving phase. The temperaturesof the moving phase, T and T′, are set, depending on the molecularweight of the polymer contained in the composition and the extractionpressure P. For instance, when the polymer contained in the compositionhas a weight average molecular weight of 1,000 to 15,000, the extractionpressure P may be in the range of from 7 MPa to 30 MPa, preferably inthe range of from 8 MPa to 25 MPa, and the temperature T is a constanttemperature of 28 degrees C. or more to less than 150 degrees C.,preferably 30 degrees C. or more to 100 degrees C. or less, furtherpreferably 30 degrees C. or more to 80 degrees or less, and thetemperature T′ is a constant temperature of 25 degrees C. or more toless than 100 degrees C., preferably 25 degrees C. or more to less than80 degrees C. or less, further preferably 25 degrees C. or more to 60degree C. or less, provided that the temperature T′ is lower than thetemperature T. In this process, the temperature may be changed in stepsbetween the temperature T and T′.

The second invention is a method for purifying the composition furthercomprising the perfluoropolyether having no carboxyl group at anyterminal, hereinafter referred to as a non-functionalizedperfluoropolyether. That is, the composition subjected to chromatographycomprises the perfluoropolyether having a carboxyl group at oneterminal, the perfluoropolyether having carboxyl groups at bothterminals and the non-functionalized perfluoropolyether. This methodcomprises the following step (i′) or (ii′).

(i′) The moving phase is at a constant temperature, T₀, of 25 degrees C.or higher to 150 degrees C. or lower and a constant pressure, P₁, of 7MPa or higher to lower than 30 MPa to thereby collect a fractioncontaining the non-functionalized perfluoropolyether at a higher ratioand, subsequently, the pressure of the moving phase is increased to aconstant temperature, P₂, which is higher than 7 MPa to 30 MPa or lowerand is higher than the aforesaid pressure P₁ to thereby collect afraction containing the perfluoropolyether having a carboxyl group atone terminal at a higher ratio. In this step, the temperature of themoving phase remains at the aforesaid temperature T₀. The temperaturemay slightly change.

(ii′) The moving phase is at a constant temperature, T₁, of higher than25 degrees C. to 150 degrees C. or lower and a constant pressure, P₀, of7 MPa or higher to 30 MPa or lower to thereby collect a fractioncontaining the non-functionalized perfluoropolyether at a higher ratioand, subsequently, the temperature of the moving phase is decreased to aconstant temperature, T₂, which is 25 degrees C. or higher to lower than150 degrees C. and is lower than the aforesaid temperature T₁ to therebycollect a fraction containing the perfluoropolyether having a carboxylgroup at one terminal at a higher ratio. In this step, the pressure ofthe moving phase remains at the aforesaid pressure P₀. The temperaturemay slightly change.

In the process comprising the aforesaid step (i′), the temperature ofthe moving phase is preferably fixed. In the process comprising theaforesaid step (ii′), the pressure of the moving phase is preferablyfixed. As stated for the aforesaid first invention, when the temperatureis fixed, the solubility of the compound having a functional group inthe moving phase is higher with a higher pressure of the moving phase.When the pressure is fixed, the solubility of the compound having afunctional group in the moving phase is higher with a lower temperatureof the moving phase. In the second invention, according to any one ofthe steps (i′) and (ii′), a fraction containing the perfluoropolyetherhaving a carboxyl group at one terminal at a higher ratio is collected.That is, the content of the perfluoropolyether having a carboxyl groupat one terminal increases in the composition.

In the second invention, the aforesaid higher ratio means that thecomposition comprising the perfluoropolyether having a carboxyl group atone terminal preferably at 80 mole % or more, more preferably 90 mole %or more, further preferably 95 mole % or more, relative to a total moleof the perfluoropolyether having a carboxyl group at one terminal, theperfluoropolyether having carboxyl groups at both terminals and thenon-functionalized perfluoropolyether. Further, the aforesaid high ratioof the non-functionalized perfluoropolyether means that the compositioncomprises the non-functionalized perfluoropolyether preferably at 90mole % or more, more preferably 95 mole % or more, further preferably100 mole %. In the present invention, the pressure of the moving phasemeans the pressure of the moving phase in a high pressure vessel and thetemperature of the moving phase means the temperature of the movingphase in a high pressure vessel.

The carbon dioxide used as a moving phase is in a supercritical orsubcritical state. Carbon dioxide has the critical temperature of 31.1degrees C. and the critical pressure of 7 MPa. In the present invention,the carbon dioxide may be in a subcritical state and not is limited tobe in a supercritical state. The pressure of the carbon dioxide in thepresent invention is in the range of from 7 MPa to 35 MPa, preferably inthe range of from 8 MPa to 30 MPa. The temperature of the carbon dioxideis in the range of from 25 degrees C. to 150 degrees C., preferably inthe range of from 30 degrees C. to 100 degrees C. The flow rate of themoving phase may be properly selected and not limited to any particularone. In a case where a volume of an extraction vessel used is large, alarge flow rate is preferred. The volume of the extraction vessel may beproperly selected, depending on an amount of the composition to bepurified.

In particular, in the aforesaid step (i′), P₁ is preferably 7 MPa ormore to 25 MPa or less, and further preferably 7 MPa or more to 22 MPaor less, and P₂ is preferably more than 7 MPa to less than 30 MPa,preferably 8 MPa or more to less than 30 MPa, and further preferably 8MPa or more to 25 MPa or less, provided that P₂ is higher than P. In theaforesaid step (ii′), T₁ is preferably 40 degrees C. or more to 150degrees C. or less, and T₂ is 28 degrees C. or more to less than 150degrees C., preferably 30 degrees C. or more to 100 degrees C. or less,further preferably 30 degrees C. or more to 80 degrees C. or less,provided that T₂ is lower than T₁.

In the second invention, the chromatography may further comprise thefollowing step (i″) after aforesaid step (i′) or the following step(ii″) after aforesaid step (ii′).

(i″) The pressure of the moving phase is increased to a constantpressure, P₃, which is higher than 7 MPa to 35 MPa or lower and ishigher than the aforesaid pressure P₂ to thereby collect a fractioncontaining the perfluoropolyether having carboxyl groups at bothterminals at a higher ratio. In this step, the temperature of the movingphase remains at the aforesaid temperature T₀. The temperature mayslightly change.

(ii″) The temperature of the moving phase is decreased to a constanttemperature, T₃, which is 25 degrees C. or higher to lower than 100degrees C. and is lower than the aforesaid temperature, T₂, to therebycollect a fraction containing the perfluoropolyether having carboxylgroups at both terminals at a higher ratio. In this step, the pressureof the moving phase remains at the aforesaid pressure P₀. Thetemperature may slightly change.

According to the aforesaid step (i″) or (ii″), a fraction containing alarger amount of the perfluoropolyether having carboxyl groups at bothterminals can be collected.

In the process comprising the aforesaid step (i′), the pressures of themoving phase P₁, P₂ and P₃ are set, depending on the molecular weight ofthe polymer contained in the composition and the extraction temperatureT₀. For instance, when the polymer contained in the composition has aweight average molecular weight of 1,000 or more to less than 3,000, theextraction temperature T₀ may be a constant temperature in the range offrom 25 degrees C. to 150 degrees C., preferably in the range of from 30degrees C. to 80 degrees C. The pressure P₁ is a constant pressure of 7MPa or more to 20 MPa or less, preferably 7 MPa or more to 15 MPa orless, and the pressure P₂ is a constant pressure of 8 MPa or more to 25MPa or less, preferably 10 MPa or more to 20 MPa or less, provided thatthe pressure P₂ is higher than the pressure P₁. In the step (i″), thepressure P₃ is a constant pressure of 10 MPa or more to 30 MPa or less,preferably 15 MPa or more to 30 MPa or less, provided that the pressureP₃ is higher than the pressure P₂.

When the polymer contained in the composition has a weight averagemolecular weight of 3,000 or more to less than 5,000, in particular3,000 or more to 4,500 or less, the extraction temperature T₀ may be aconstant temperature in the range of from 25 degrees C. to 150 degreesC., preferably in the range of from 30 degrees C. to 80 degrees C. Thepressure P₁ is a constant pressure of 7 MPa or more to 20 MPa or less,preferably 8 MPa or more to 18 MPa or less, and the pressure P₂ is aconstant pressure of 8 MPa or more to 27 MPa or less, preferably 10 MPaor more to 22 MPa or less, provided that the pressure P₂ is higher thanthe pressure P₁. In the step (i″), the pressure P₃ is a constantpressure 10 MPa or more to 30 MPa or less, preferably 15 MPa or more to30 MPa or less, provided that the pressure P₃ is higher than thepressure P₂.

When the polymer contained in the composition has a weight averagemolecular weight of 5,000 or more to 7,000 or less, the extractiontemperature T₀ may be a constant temperature in the range of from 25degrees C. to 150 degrees C., preferably in the range of from 30 degreesC. to 80 degrees C. The pressure P₁ is a constant pressure of 7 MPa ormore to 22 MPa or less, preferably 8 MPa or more to 20 MPa or less, andthe pressure P₂ is a constant pressure of 8 MPa or more to 30 MPa orless, preferably 10 MPa or more to 25 MPa or less, provided that thepressure P₂ is higher than the pressure P₁. In the step (i″), thepressure P₃ is a constant pressure of 10 MPa or more to 30 MPa or less,preferably 15 MPa or more to 30 MPa or less, provided that the pressureP₃ is higher than the pressure P₂.

In the process comprising the aforesaid step (ii′), the temperatures ofthe moving phase T₁, T₂ and T₃ are set depending on the molecular weightof the polymer comprised in the composition and the extraction pressureP₀. For instance, when the polymer contained in the composition has aweight average molecular weight of 3,000 to 5,000, the extractionpressure P₀ may be a constant pressure in the range of from 7 MPa to 30MPa, preferably in the range of from 8 MPa to 25 MPa. The temperature T₁is a constant temperature of 40 degrees C. or more to 150 degrees C. orless, preferably 50 degrees C. or more to 100 degrees C. or less, andthe temperature T₂ is a constant temperature of 30 degrees C. or more to100 degrees C. or less, preferably 35 degrees C. or more to 90 degreesC. or less, further preferably 40 degrees C. or more to 80 degree C. orless, provided that the temperature T₂ is lower than the temperature T₁.In the step (ii″), the temperature T₃ is a constant temperature of 25degrees C. or more to less than 100 degrees C., preferably 25 degrees C.or more to 60 degrees C. or less, provided that the temperature T₃ islower than the temperature T₂.

In the methods of the first and second inventions, periods to collectfractions may be properly decided, depending on molecular weights andamounts of the polymers in the composition. For instance, structures ofcompounds contained in fractions may be monitored. Monitoring may beconducted by IR absorption.

The stationary phase used in the methods of first and second inventionsis silica gel. The silica gel may be properly selected from commercialproducts. The silica gel is preferably spherical. A particle diameter ofthe silica gel is preferably 30 to 300 μm, further preferably 40 to 100μm. The silica gel has preferably pH in a range between a weak acid andneutral. The silica gel preferably has pH between 5 and 7.5, furtherpreferably 6.5 and 7.5, as determined on a water dispersion at 25degrees C. containing 10 weight % of the silica gel. If basic silica gelis used, a carboxyl group in the perfluoropolyether is trapped by thesilica gel, so that the perfluoropolyether having a carboxyl group maynot be collected. The aforesaid determination of pH is as the JapaneseIndustrial Standards (JIS) Z 0701, Silicagel Desiccants for Packaging.

When an anion-exchange resin as described in Patent Literature 3 is usedas a stationary phase, a fraction containing the perfluoropolyetherhaving a carboxyl group at one terminal at a higher ratio cannot beobtained. In contrast, on account of the use of the aforesaid silica gelas a stationary phase, a fraction containing the perfluoropolyetherhaving a carboxyl group at one terminal at a higher ratio can beobtained.

Composition Comprising Perfluoropolyether Having a Carboxyl Group at OneTerminal

One of the compositions used in the present method comprises theperfluoropolyether having a carboxyl group at one terminal and theperfluoropolyether having carboxyl groups at both terminals. The othercomposition used in the present method comprises the perfluoropolyetherhaving a carboxyl group at one terminal, the perfluoropolyether havingcarboxyl groups at both terminals, and the perfluoropolyether having nofunctional group at any terminal. A functional group at the terminal ofthe compound in a composition subjected to chromatography according tothe present method needs to have carboxyl groups in advance.

The perfluoropolyether has a polyfluorooxyalkylene structure which hasplural repeating units represented by the formula: —C_(j)F_(2j)O—,wherein j is an integer of 1 or more, preferably an integer of from 1 to6, preferably 1 to 4. In particular, the polyfluorooxyalkylene structurehas 10 to 500, preferably 15 to 200, more preferably 20 to 100, furtherpreferably 25 to 80 repeating units.

The repeating unit, —C_(j)F_(2j)O—, may be linear or branched. Examplesof the repeating unit include the following, where thepolyfluorooxyalkylene structure may be a combination of two or morekinds of the following units.

—CF₂O— —CF₂CF₂O— —CF₂CF₂CF₂O— —CF(CF₃)CF₂O— —CF₂CF₂CF₂CF₂O——CF₂CF₂CF₂CF₂CF₂O— —C(CF₃)₂O—

The aforesaid polyfluorooxyalkylene structure is particularly onesrepresented by the following formula:

—(CF₂)_(d)—(OCF₂)_(p)(OCF₂CF₂)_(q)(OCF₂CF₂CF₂)_(r)(OCF₂CF₂CF₂CF₂)_(s)—O(CF₂)_(d)—,

wherein d is an integer of from 0 to 5, p and q are, independently ofeach other, an integer of from 5 to 300, r and s are, independently ofeach other, an integer of from 0 to 100, and a total of p, q, r and s is10 to 500, preferably 15 to 200, and the parenthesized units may besequenced at random.

The perfluoropolyether having a carboxyl group at one terminal has theaforesaid polyfluorooxyalkylene structure and a carboxyl group at oneterminal. For instance, the compound is represented by the followingformula (a):

A-Rf—B  (a)

wherein Rf is a linear or branched polyfluorooxyalkylene group which mayhave 10 to 500, preferably 15 to 200, more preferably 20 to 100, furtherpreferably 25 to 80 repeating units, represented by the formula:—OC_(j)F_(2j)O—, wherein j is as defined above.

The Rf is particularly represented by the following formula:

—(CF₂)_(d)—(OCF₂)_(p)(OCF₂CF₂)_(q)(OCF₂CF₂CF₂)_(r)(OCF₂CF₂CF₂CF₂)_(s)—O(CF₂)_(d)—

wherein d, p, q, r and s are as defined above.

Further, it is preferable that the Rf has 5 to 80 units represented bythe formula (OCF₂) and 5 to 80 units represented by the formula(OCF₂CF₂) and a total number of the units (OCF₂) and (OCF₂CF₂) is 20 to150.

In the formula (a), A and B are a carboxyl group or a —CF₃ group andeither of A and B is a carboxyl group.

The perfluoropolyether having carboxyl groups at both terminals has theaforesaid polyfluorooxyalkylene structure and carboxyl groups at theboth terminals. For instance, the compound is represented by thefollowing formula (b):

HOOC—Rf—COOH  (b)

wherein Rf is as defined above.

The non-functionalized perfluoropolyether has the aforesaidpolyfluorooxyalkylene structure and no carboxyl group at any terminal.For instance, the compound is represented by the following formula (c):

F₃C—Rf—CF₃  (c)

wherein Rf is as defined above.

The composition comprising the perfluoropolyether having a carboxylgroup at one terminal is prepared by fluorinating a part of terminalgroups of perfluoropolyethers having functional groups at the bothterminals. The fluorination can be controlled by adjusting the amount ofthe fed fluorine gas to thereby control the percentage of thefluorination. The number of the CF₃ group introduced is preferably 50 to90%, further preferably 60 to 90%, particularly 65 to 85%, relative to atotal number of the terminal groups. If the ratio of the fluorination issmaller than the aforesaid lower limit, the ratio of the both-terminalfunctionalized polymer increases. If the ratio of the fluorination islarger than the aforesaid upper limit, the ratio of thenon-functionalized polymer increases. Therefore, the ratio of theone-terminal functionalized polymer decreases and that is notpreferable.

In particular, the ratio of the perfluoropolyether having carboxylgroups at both terminals in the composition before subjected tochromatography is preferably 35 mole % or less, more preferably 30 mole% or less, further preferably 20 mole % or less, further preferably 15mole % or less, relative to a total amount of the the perfluoropolyetherhaving carboxyl groups at both terminals and the perfluoropolyetherhaving a carboxyl group at one terminal. Then, it is more secured toobtain a fraction containing 85 mole % or more, preferably 90 mole % ormore, further preferably 95 mole % or more of the perfluoropolyetherhaving a carboxyl group at one terminal.

The perfluoropolyether having a carboxyl group at one terminal isprepared, for instance, by fluorinating a part of carboxyl groups ofperfluoropolyether having carboxyl groups at the both terminals.Alternatively, it is prepared by fluorinating a part of non-carboxylfunctional groups of a perfluoropolyether having the functional groupsat the both terminals and, then, converting the remaining functionalgroup into a carboxyl group. The non-carboxyl functional group may be ahydroxyl group, an ester group, an acid chloride group and an acidfluoride group. Among them, an acid fluoride group, i.e. —C(═O)—F, ispreferable. The conversion of the functional group into a carboxyl groupmay be conducted in any conventional manners. For instance, the acidfluoride group is reacted with water to give a carboxyl group.

The present method allows one to efficiently and easily prepare, acomposition comprising the perfluoropolyether having a carboxyl group atone terminal at a higher ratio, preferably 80% or more, more preferably90% or more, further preferably 95% or more. Further, according to thepresent method, a composition comprising the perfluoropolyether having acarboxyl group at one terminal at a higher molar ratio can be preparedfrom the perfluoropolyether introduced functional groups at the bothterminals as a starting compound, even in the case where theperfluoropolyether has a structure such that it is difficult to directlyintroduce a functional group at only one terminal. In the presentmethod, the molecular weight of the polymer is not limited to anyparticular one as long as the polymer is soluble in carbon dioxide and,therefore, the present method can be applied to polymers having a widemolecular weight. In particular, the present method is preferablyapplied to a purification of a perfluoropolyether having a weightaverage molecular weight of 1,000 to 100,000, further preferably 1,000to 15,000.

As stated above, the separation and purification method with anion-exchange resin, as described in Patent Literature 3, uses largeamounts of a fluorine solvent and hydrochloric acid and, therefore, isunsuitable to mass production. Purification by thin-film distillationcannot provide a composition, at a higher ratio, containingperfluoropolyether having a carboxyl group at one terminal; andtherefore, when the composition is produced in large quantities, mayhave poor properties. In contrast, the present method is suitable to themass production and efficiently provides a composition having goodproperties. Accordingly, the present method is useful for thepreparation of starting materials for surface treatment agents,lubricants and elastomers.

For instance, a group having a hydrolyzable group is introduced to thecarboxyl group at the terminal of the perfluoropolyether in thecomposition obtained in the present method to thereby provide acomposition containing at a higher ratio a perfluoropolyether having ahydrolyzable group at one terminal. The composition is suitable as asurface treatment agent. Further, the perfluoropolyether having acarboxyl group at one terminal may be converted into derivatives such asacryl, amine or isocyanate derivatives in any publicly known manner.

A group having the hydrolyzable group is, for instance, represented bythe following formula:

wherein R is an alkyl group having 1 to 4 carbon atoms or phenyl group,X is a hydrolyzable group and a is 2 or 3.

In the afore-mentioned formula (1), X is, independently of each other,any hydrolyzable group. Examples of X include alkoxy groups having 1 to10 carbon atoms such as methoxy, ethoxy, propoxy and buthoxy groups;oxyalkoxy groups having 2 to 10 carbon atoms such as methoxymethoxy andmethoxyethoxy groups; acyloxy groups having 1 to 10 carbon atoms such asan acetoxy group; alkenyloxy groups having 2 to 10 carbon atoms such asan isopropenoxy group; and halogen atoms such as chlorine, bromine, andiodine atoms. Among these, methoxy, ethoxy, isopropenoxy groups and achlorine atom are preferred.

R is preferably a methyl group. “a” is preferably 3 in view of thereactivity and the adhesiveness to a substrate.

The perfluoropolyether having a hydrolyzable group at one terminal andhaving the aforesaid group represented by the formula (1) may berepresented by the following formula (2):

wherein Rf is as defined above, A is a —CF₃ group, Q is a divalentorganic group, Z is a divalent to octavalent organopolysiloxane moietyhaving siloxane bonds, R and X are as defined above, a is 2 or 3, b isan integer of from 1 to 7, c is an integer of from 1 to 10, and α is 0or 1.

In the afore-mentioned formula (2), Q is a linking group to connect Rfwith Z, or Rf with the (CH₂), group, preferably an organic group having2 to 12 carbon atoms which may have one or more bonds selected from anamide bond, an ether bond, an ester bond and a vinyl bond. Preferred isa substituted or unsubstituted divalent hydrocarbon group having 2 to 12carbon atoms which may have one or more bonds selected from an amidebond, an ether bond, an ester bond and a vinyl bond. Examples of Qinclude the following:

In the afore-mentioned formula (2), Z is a divalent to octavalentorganopolysiloxane moiety having siloxane bonds. Z is preferably a lineror cyclic organopolysiloxane moiety having 2 to 13 silicon atoms,preferably 2 to 5 silicon atoms. Z may contain a silalkylene structurewhere two silicon atoms are bonded via an alkylene group, that is,Si—(CH₂)_(n)—Si, wherein n is preferably an integer of from 2 to 6.

Preferably, the organopolysiloxane moiety has an alkyl group having 1 to8 carbon atoms, preferably 1 to 4 carbon atoms, or phenyl group. Thealkylene group in the silalkylene bond preferably has 2 to 6 carbonatoms, more preferably 2 to 4 carbon atoms.

Examples of Z include the following;

The introduction of the hydrolyzable group may be carried out accordingto any conventional method, for instance, the methods described inJapanese Patent Application Laid-Open No. 2012-72272, Patent Literature3, and Japanese Patent Application Laid-Open No. 2012-233157, PatentLiterature 2. For instance, the hydrolyzable group is introduced by thefollowing steps (1) to (3).

(1) The terminal carboxyl group of the perfluoropolyether in thecomposition is reduced with a metal hydride or in a catalytichydrogenation with a precious metal catalyst to convert apart ofcarboxyl groups into hydroxyl groups. Examples of the metal hydrideinclude sodium bis (2-methoxyethoxy)aluminium hydride. Examples of theprecious metal catalyst include ruthenium.

(2) Then, a compound having an aliphatic unsaturated group is reactedwith the terminal hydroxyl group of the perfluoropolyether according toany conventional publicity known method. The aliphatic unsaturated groupmay be, for instance, an alkenyl group having 2 to 12 carbon atoms. Forexample, the mixture of perfluoropolyethers obtained in the aforesaidstep (1) is reacted with an alkenyl halide such as ally bromide in thepresence of tetrabutylammonium hydrogen sulfate, to which sodiumhydroxide solution is then added dropwise to make the reaction mixturealkaline to thereby introduce an allyl group at the terminal of thepolymer.

(3) Subsequently, a hydrolyzable silyl group is introduced at thealiphatic unsaturated terminal group. This is done by an additionreaction of the perfluoropolyether obtained in the aforesaid step (2)with an organosilicon compound having an SiH group at one terminal and ahydrolyzable group, X, at the other terminal. Examples of theorganosilicon compound include a terminal hydrolyzable group-containingorganohydrogensilane. The addition reaction may be carried out in thepresence of an addition reaction catalyst, such as a platinum compound,according to any conventional method.

According to the aforesaid steps, the composition containing theperfluoropolyether having a hydrolyzable group at one terminal,represented by the formula (2), at a higher ratio can be prepared. Thiscomposition is suitable as a surface treatment agent.

The surface treatment agent may comprise a partial hydrolysis andcondensation product of the perfluoropolyether represented by theaforesaid formula (2). The partial hydrolysis and condensation isobtained by subjecting a part of the terminal hydrolyzable group (s) ofthe perfluoropolyether represented by the aforesaid formula (2) to ahydrolysis and condensation reaction in a conventional manner.

The surface treatment agent may contain a catalyst for a hydrolysis andcondensation reaction. Examples of the catalyst include organic tincompounds such as dibutyltin dimethoxide and dibutyltin dilaurate;organic titanium compounds such as tetra-n-butyl titanate; organic acidssuch as acetic acid, methanesulfonic acid and fluorinated carboxylicacid; and inorganic acids such as hydrochloric acid and sulfuric acid.Among these, preferred are acetic acid, tetra-n-butyltitanate,dibutyltin dilaurate and fluorinated carboxylic acid. A content of thecatalyst may be a catalytic amount, which ranges typically from 0.01 to5 parts by mass, particularly from 0.05 to 1 part by mass, relative to100 parts by mass of the perfluoropolyether and/or the partialhydrolysis and condensation product of the perfluoropolyether.

The surface treatment agent may contain a solvent. Examples of thesolvent include fluorinated aliphatic hydrocarbon solvents such asperfluoroheptane and perfluorooctane; fluorinated aromatic hydrocarbonsolvents such as m-xylenehexafluoride, benzotrifluoride and1,3-bis(trifluoromethyl)benzene; fluorinated ether solvents such asmethyl perfluorobutyl ether, ethyl perfluorobutyl ether, andperfluoro(2-butyltetrahydrofuran); fluorinated alkylamine solvents suchas perfluorotributylamine and perfluorotripentylamine; hydrocarbonsolvents such as petroleum benzene, mineral spirits, toluene, andxylene; ketone solvents such as acetone, methylethylketone, andmethylisobutylketone. Among these, fluorinated solvents are preferred inview of solubility and wettability of the composition. Particularlypreferred are 1,3-bis(trifluoromethyl)benzene, m-xylenehexafluoride,perfluoro(2-butyltetrahydrofuran), perfluorotributylamine and ethylperfluorobutyl ether.

A mixture of two or more of the aforesaid solvents may be used.Preferably, the perfluoropolyether or the partial hydrolysis andcondensation product of the perfluoropolyether is homogeneouslydissolved. An optimum concentration of the perfluoropolyether in thesolvent may be decided, depending on treatment conditions, and isusually from 0.01 to 30 wt %, preferably from 0.02 to 20 wt %, furtherpreferably from 0.05 to 5 wt %, but not limited to these.

The surface treatment agent may be applied to a substrate by vapordeposition to form a coating having good properties. The vapordeposition may be made by, for instance, resistance heating orelectron-beam heating, but not be limited to them. The curing conditionsmay be selected properly, depending on the surface-treating manner. Whenthe composition is applied by spraying, ink-jetting, brushing ordipping, a curing temperature is preferably in a range of roomtemperature, i.e. 20 plus or minus 15 degrees C., and 100 degrees C. Thecuring is carried out preferably in a humid environment to promote thecuring reaction. A thickness of a cured coating may be selected,depending on a type of a substrate, and is typically from 0.1 nm to 100nm, particularly from 1 to 20 nm.

The substrate material to be treated with the surface treatment agentmay be of a various types, such as paper, cloths, metals and metaloxides, glass, plastics, ceramics and quartz, but is not limited tothese. The present surface treatment agent can provide water- andoil-repellency, a low dynamic friction coefficient or scratch resistanceto these substrate materials. In particular, the surface treatment agentis suitable for glass which is treated with SiO₂ or plasma, or quartzsubstrates.

Examples of articles to be treated with the surface treatment agentinclude glass, hard coat films, high hardness films, anti-reflectionfilms, lenses of spectacles, optical lenses and quartz substrates. Inparticular, the surface treatment agent is useful for forming a water-and oil-repellent coating on a surface of toughened glasses oranti-reflective coating glasses.

EXAMPLES

The present invention will be explained in detail by reference to theExamples and the Comparative Examples, but shall not be limited thereto.In the following Examples and Comparative Examples, a pressure of themoving phase means a pressure of the moving phase in a high pressurevessel and a temperature of the moving phase means a temperature of themoving phase in a high pressure vessel. The pH of the silica gel wasdetermined according to the Japanese Industrial Standards (JIS) Z 0701,Silicagel Desiccants for Packaging, as pH of a water dispersioncontaining 10 weight % of the silica gel. Specifically, 200 ml ofdistilled water was added to 20 g of silica gel, the mixture was heatedat 80 degrees C. for 30 minutes and, then, cooled to room temperatureand, subsequently, the supernatant was subjected to JIS Z 8802, Methodsfor determination of pH, to determine pH.

In the Examples and the Comparative Examples, mixtures of the followingcompounds (1a), (1b) and (1c) were used, hereinafter referred to ascompositions F50, F60, F70, F80 and F90. These mixtures were prepared bypartially fluorinating carboxyl groups of perfluoropolyethersrepresented by the following formula (1b) using fluorine gas. Themixtures having the ratio, mole %, described in the following table 1were prepared by adjusting the amount of the fed fluorine gas. Thepolymers having a carboxylic group(s) were adsorbed to an acid adsorbentto be separated and, then, a ratio of the polymers described in Table 1was determined according to ¹⁹F-NMR analysis.

F₃C(OC₂F₄)_(p)(OCF₂)_(q)—OCF₂COOH  (1a)

HOOC—CF₂—(OC₂F₄)_(p)(OCF₂)_(q)—OCF₂COOH  (1b)

F₃C(OC₂F₄)_(p)(OCF₂)_(q)—OCF₃  (1c)

(p/q=0.9, p+q was approximately 45)

TABLE 1 Ratio of a Fluorination compound, mole % Composition Ratio, %(1a) (1b) (1c) F50 50 52 24 24 F60 60 56 12 32 F70 70 48 6 46 F80 80 343 63 F90 90 18 1 81

Example 1

Grams of composition F60 were passed through a 25-millilitre highpressure vessel which was filled with silica gel 60 N, ex Kanto ChemicalCo., Ltd., in a dry particle packing method and a supercritical statecarbon dioxide was used as a moving phase. The pH of the silica gel at25 degrees C. was between 6.5 and 7.5 and the particle diameter of thesilica gel was 40 to 100 μm. The flow rate of the moving phase was 15ml/min and the temperature was 40 degrees C.

The pressure was increased from 8 MPa to 25 MPa, as explained below.First, supercritical state carbon dioxide of 40 degrees C. and 8 MPa waspassed through the high pressure vessel. Then, the pressure of themoving phase was increased to 12 MPa. A fraction was collected at 12 MPafor 60 minutes. Subsequently, the pressure of the moving phase wasincreased to 18 MPa to collect a fraction for 60 minutes and, then, thepressure of the moving phase was increased to 25 MPa to collect afraction for 60 minutes. Molar ratios of the components in each fractionwere as shown in Table 2. The molar ratios of the components in eachfraction were determined by ¹⁹F-NMR analysis.

TABLE 2 Amount of a composition Molar ratio of a Pressure, Time, in acompound, % MPa minutes fraction, g (1a) (1b) (1c) 12 60 3.0 0 0 100 1860 4.6 92 8 1 25 60 1.0 35 65 0

Example 2

Grams of composition F70 were passed through a 25-millilitre highpressure vessel which was filled with silica gel 60 N, ex Kanto ChemicalCo., Ltd., in a dry particle packing method and a supercritical statecarbon dioxide was used as a moving phase. The pH of the silica gel at25 degrees C. was between 6.5 and 7.5 and the particle diameter of thesilica gel was 40 to 100 μm. The flow rate of the moving phase was 15ml/min and the temperature was 40 degrees C.

The pressure was increased from 8 MPa to 25 MPa, as explained below.First, supercritical state carbon dioxide of 40 degrees C. and 8 MPa waspassed through the high pressure vessel. Then, the pressure of themoving phase was increased to 12 MPa. A fraction was collected at 12 MPafor 60 minutes. Subsequently, the pressure of the moving phase wasincreased to 18 MPa to collect a fraction for 60 minutes and, then, thepressure of the moving phase was increased to 25 MPa to collect afraction for 60 minutes. Molar ratios of the components in each fractionwere as shown in Table 3. The molar ratios of components were determinedby ¹⁹F-NMR analysis. An amount of a composition collected at 25 MPa wastoo small to analyze the molar ratio.

TABLE 3 Amount of a composition Molar ratio of a Pressure, Time, in acompound, % MPa minutes fraction, g (1a) (1b) (1c) 12 60 4.3 0 0 100 1860 4.0 96 3 1 25 60 0.8 — — —

Example 3

Grams of composition F80 were passed through a 25-millilitre highpressure vessel which was filled with silica gel 60 N, ex Kanto ChemicalCo., Ltd., in a dry particle packing method and a supercritical statecarbon dioxide was used as a moving phase. The pH of the silica gel at25 degrees C. was between 6.5 and 7.5 and the particle diameter of thesilica gel was 40 to 100 μm. The flow rate of the moving phase was 15ml/min and the temperature was 40 degrees C.

The pressure was increased from 8 MPa to 25 MPa, as explained below.First, supercritical state carbon dioxide of 40 degrees C. and 8 MPa waspassed through the high pressure vessel. Then, the pressure of themoving phase was increased to 12 MPa. A fraction was collected at 12 MPafor 60 minutes. Subsequently, the pressure of the moving phase wasincreased to 18 MPa to collect a fraction for 60 minutes and, then, thepressure of the moving phase was increased to 25 MPa to collect afraction for 60 minutes. Molar ratios of the components in each fractionwere as shown in Table 4. The molar ratios of components were determinedby ¹⁹F-NMR analysis. An amount of a composition collected at 25 MPa wastoo small to analyze the component.

TABLE 4 Amount of a composition Molar ratio of a Pressure, Time, in acompound, % MPa minutes fraction, g (1a) (1b) (1c) 12 60 6.0 0 0 100 1860 2.9 98 1 1 25 60 0.3 — — —

Example 4

Grams of composition F90 were passed through a 25-millilitre highpressure vessel which was filled with silica gel 60 N, ex Kanto ChemicalCo., Ltd., in a dry particle packing method and a supercritical statecarbon dioxide was used as a moving phase. The pH of the silica gel at25 degrees C. was between 6.5 and 7.5 and the particle diameter of thesilica gel was 40 to 100 μm. The flow rate of the moving phase was 15ml/min and the temperature was 40 degrees C.

The pressure was increased from 8 MPa to 25 MPa, as explained below.First, supercritical state carbon dioxide of 40 degrees C. and 8 MPa waspassed through the high pressure vessel. Then, the pressure of themoving phase was increased to 12 MPa. A fraction was collected at 12 MPafor 60 minutes. Subsequently, the pressure of the moving phase wasincreased to 18 MPa to collect a fraction for 60 minutes and, then, thepressure of the moving phase was increased to 25 MPa to collect afraction for 60 minutes. Molar ratios of the components in each fractionwere as shown in Table 5. The molar ratios of components were determinedby ¹⁹F-NMR analysis. An amount of a composition collected at 25 MPa wastoo small to analyze the component.

TABLE 5 Amount of a composition Molar ratio of a Pressure, Time, in acompound, % MPa minutes fraction, g (1a) (1b) (1c) 12 60 7.8 0 0 100 1860 1.5 98 1 1 25 60 0.1 — — —

Example 5

In the Example 5, a mixture of 50 mole % of the following compound (2a),5 mole % of the following compound (2b) and 45 mole % of the followingcompound (2c) was used.

F₃C(OC₂F₄)_(p)(OCF₂)_(q)—OCF₂COOH  (2a)

HOOC—CF₂—(OC₂F₄)_(p)(OCF₂)_(q)—OCF₂COOH  (2b)

F₃C(OC₂F₄)_(p)(OCF₂)_(q)—OCF₃  (2c)

(p/q=0.9, p+q was approximately 23)

10 Grams of the mixture were passed through a 25-millilitre highpressure vessel which was filled with silica gel 60 N, ex Kanto ChemicalCo., Ltd., in a dry particle packing method and a supercritical statecarbon dioxide was used as a moving phase. The pH of the silica gel at25 degrees C. was between 6.5 and 7.5 and the particle diameter of thesilica gel was 40 to 100 μm. The flow rate of the moving phase was 15ml/min and the temperature was 40 degrees C.

The pressure was increased from 8 MPa to 25 MPa, as explained below.First, supercritical state carbon dioxide of 40 degrees C. and 8 MPa waspassed through the high pressure vessel. Then, the pressure of themoving phase was increased to 10 MPa. A fraction was collected at 10 MPafor 60 minutes. Subsequently, the pressure of the moving phase wasincreased to 15 MPa to collect a fraction for 60 minutes and, then, thepressure of the moving phase was increased to 25 MPa to collect afraction for 60 minutes. Molar ratios of the components in each fractionwere as shown in Table 6. The molar ratios of components were determinedby ¹⁹F-NMR analysis. An amount of a composition collected at 25 MPa wastoo small to analyze the component.

TABLE 6 Amount of a composition Molar ratio of a Pressure, Time, in acompound, % MPa minutes fraction, g (1a) (1b) (1c) 10 60 4.3 0 0 100 1560 4.8 97 2 1 25 60 0.3 — — —

Example 6

In the Example 6, a mixture of 52 mole % of the following compound (3a),5 mole % of the following compound (3b) and 43 mole % of the followingcompound (3c) was used.

F₃C(OC₂F₄)_(p)(OCF₂)_(q)—OCF₂COOH  (3a)

HOOC—CF₂—(OC₂F₄)_(p)(OCF₂)_(q)—OCF₂COOH  (3b)

F₃C(OC₂F₄)_(p)(OCF₂)_(q)—OCF₃  (3c)

(p/q=0.9, p+q was approximately 60)

10 Grams of the mixture were passed through a 25-millilitre highpressure vessel which was filled with silica gel 60 N, ex Kanto ChemicalCo., Ltd., in a dry particle packing method and a supercritical statecarbon dioxide was used as a moving phase. The pH of the silica gel at25 degrees C. was between 6.5 and 7.5, and the particle diameter of thesilica gel was 40 to 100 μm. The flow rate of the moving phase was 15ml/min, and the temperature was 40 degrees C.

The pressure was increased from 8 MPa to 25 MPa, as explained below.First, supercritical state carbon dioxide of 40 degrees C. and 8 MPa waspassed through the high pressure vessel. Then, the pressure of themoving phase was increased to 14 MPa. A fraction was collected at 14 MPafor 60 minutes. Subsequently, the pressure of the moving phase wasincreased to 20 MPa to collect a fraction for 60 minutes and, then, thepressure of the moving phase was increased to 25 MPa to collect afraction for 60 minutes. Molar ratios of the components in each fractionwere as shown in Table 7. The molar ratios of components were determinedby ¹⁹F-NMR analysis. An amount of a composition collected at 25 MPa wastoo small to analyze the component.

TABLE 7 Amount of a composition Molar ratio of a Pressure, Time, in acompound, % MPa minutes fraction, g (1a) (1b) (1c) 14 60 4.0 0 0 100 2060 4.9 96 3 1 25 60 0.2 — — —

Example 7

Grams of composition F50 were passed through a 25-millilitre highpressure vessel which was filled with silica gel 60 N, ex Kanto ChemicalCo., Ltd., in a dry particle packing method and a supercritical statecarbon dioxide was used as a moving phase. The pH of the silica gel at25 degrees C. was between 6.5 and 7.5 and the particle diameter of thesilica gel was 40 to 100 μm. The flow rate of the moving phase was 15ml/min and the temperature was 40 degrees C.

The pressure was increased from 8 MPa to 25 MPa, as explained below.First, supercritical state carbon dioxide of 40 degrees C. and 8 MPa waspassed through the high pressure vessel. Then, the pressure of themoving phase was increased to 12 MPa. A fraction was collected at 12 MPafor 60 minutes. Subsequently, the pressure of the moving phase wasincreased to 18 MPa to collect a fraction for 60 minutes and, then, thepressure of the moving phase was increased to 25 MPa to collect afraction for 60 minutes. Molar ratios of the components in each fractionwere as shown in Table 8. The molar ratios of components were determinedby ¹⁹F-NMR analysis.

TABLE 8 Amount of a composition Molar ratio of a Pressure, Time, in acompound, % MPa minutes fraction, g (1a) (1b) (1c) 12 60 2.0 0 0 100 1860 4.0 88 11 1 25 60 1.3 32 68 0

The starting composition F50 was composed of 24 mole % of theperfluoropolyether having carboxyl groups at the both terminals,relative to the total moles of the perfluoropolyethers, that is, 31.5mole %, relative to the total moles of the perfluoropolyether having acarboxyl group at one terminal and the perfluoropolyether havingcarboxyl groups at both terminals. In one of the fractions collected inthe purification of this composition, the ratio of theperfluoropolyether having a carboxyl group at one terminal was 88 mole%. As seen from the results, when the starting composition comprises alarger amount of the perfluoropolyether having carboxyl groups at theboth terminals, the molar ratio of the perfluoropolyether having acarboxyl group at one terminal decreases. Therefore, in order to collecta fraction containing 90 mole % or more of the perfluoropolyether havinga carboxyl group at one terminal, it is preferred that the molar ratioof the perfluoropolyether having carboxyl groups at the both terminalsin the starting composition is 30 mole % or less.

Example 8

10 Grams of composition F70 were passed through a 25-millilitre highpressure vessel which was filled with silica gel 60 N, ex Kanto ChemicalCo., Ltd., in a dry particle packing method and a supercritical statecarbon dioxide was used as a moving phase. The pH of the silica gel at25 degrees C. was between 6.5 and 7.5 and the particle diameter of thesilica gel was 40 to 100 μm. The flow rate of the moving phase was 5ml/min and the pressure was 13 MPa.

The temperature was decreased from 80 degrees C. to 30 degrees C., asexplained below. First, supercritical state carbon dioxide of 80 degreesC. and 13 MPa was passed through the high pressure vessel. A fractionwas collected at 80 degrees C. and 13 MPa for 60 minutes. Subsequently,the temperature of the moving phase was decreased to 35 degrees C. tocollect a fraction for 60 minutes. Molar ratios of the components ineach fraction were as shown in Table 9. The molar ratios of componentswere determined by ¹⁹F-NMR analysis.

TABLE 9 Amount of a composition Molar ratio of a Pressure, Time, in acompound, % MPa minutes fraction, g (1a) (1b) (1c) 80 60 4.0 0 0 100 3560 5.1 95 3 2

Example 9

10 Grams of composition F70 were passed through a 25-millilitre highpressure vessel which was filled with silica gel 60, ex Kanto ChemicalCo., Ltd., in a dry particle packing method and a supercritical statecarbon dioxide was used as a moving phase. The pH of the silica gel at25 degrees C. was between 5.0 and 7.0, and the particle diameter of thesilica gel was 40 to 100 μm. The flow rate of the moving phase was 15ml/min, and the temperature was 40 degrees C.

The pressure was increased from 8 MPa to 25 MPa, as explained below.First, supercritical state carbon dioxide of 40 degrees C. and 8 MPa waspassed through the high pressure vessel. Then, the pressure of themoving phase was increased to 12 MPa. A fraction was collected at 12 MPafor 60 minutes. Subsequently, the pressure of the moving phase wasincreased to 18 MPa to collect a fraction for 60 minutes and, then, thepressure of the moving phase was increased to 25 MPa to collect afraction for 60 minutes. Molar ratios of the components in each fractionwere as shown in Table 10. The molar ratios of components weredetermined by ¹⁹F-NMR analysis. An amount of a composition collected at25 MPa was too small to analyze the molar ratio.

TABLE 10 Amount of a composition Molar ratio of a Pressure, Time, in acompound, % MPa minutes fraction, g (1a) (1b) (1c) 12 60 4.7 6 0 94 1860 4.3 95 3 2 25 60 0.5 — — —

As shown in Examples 1 to 9, according to the present method, a fractioncontaining the perfluoropolyether having a carboxyl group at oneterminal at a higher molar ratio is efficiently and easily collected.Thus, a content of the perfluoropolyether having a carboxyl group at oneterminal is increased in the composition. In particular, by controllinga molar ratio of the perfluoropolyether having carboxyl groups at bothterminals in a starting composition, the molar ratio of theperfluoropolyether having a carboxyl group at one terminal is increasedto 90 mole % or more, further 95 mole % or more.

Comparative Example 1

Composition F70 was passed through a 25-millilitre high pressure vesselwhich was filled with a supercritical state carbon dioxide as a movingphase, without silica gel. The flow rate of the moving phase was 15ml/min, and the temperature was 50 degrees C.

The pressure was increased from 8 MPa to 20 MPa, as explained below.First, the supercritical state carbon dioxide of 50 degrees C. and 8 MPawas passed through the high pressure vessel. Then, the pressure of themoving phase was increased to 13 MPa. A fraction was collected at 13 MPafor 30 minutes. Subsequently, the pressure of the moving phase wasincreased to 14 MPa to collect a fraction for 30 minutes, then, thepressure of the moving phase was increased to 15 MPa to collect afraction for 60 minutes and, then, the pressure of the moving phase wasincreased to 20 MPa to collect a fraction for 60 minutes. Molar ratiosof the components in each fraction are as shown in Table 11.

TABLE 11 Amount of a composition Molar ratio of a Pressure, Time, in acompound, % MPa minutes fraction, g (1a) (1b) (1c) 13 30 1.5 31 4 67 1430 4.0 45 5 52 15 60 3.5 50 7 43 20 60 0.8 51 6 43

As shown in table 11, when the silica gel was not used, the molar ratioof the perfluoropolyether having a carboxyl group at one terminal in thefaction was not 80 mole % or more in any of the fractions. This isbecause the polymers tend to be separated depending on a difference inthe molecular weight in supercritical extraction without any stationaryphase, rather than a difference in the terminal group. In this case, inorder to increase a content of the perfluoropolyether having a carboxylgroup at one terminal in a fraction, it is necessary to make themolecular weight distribution of the perfluoropolyether narrower orintroduce a so large size group at the terminal of theperfluoropolyether as to influence solubility in a supercritical statecarbon dioxide. In contrast, according to the present method, a fractioncontaining the perfluoropolyether having a carboxyl group at oneterminal at a higher ratio is efficiently collected.

Comparative Example 2

Composition F70 was passed through a 25-millilitre high pressure vesselwhich was filled with an anion-exchange resin B-20HG, ex OrganoCorporation, and a supercritical state carbon dioxide was used as amoving phase. The flow rate of the moving phase was 15 ml/min and thetemperature was 40 degrees C. The pressure was increased from 8 MPa to25 MPa. Thus, the pressure of the moving phase was increased from 8 MPato 12 MPa, then to 18 MPa, and then to 25 MPa, as in Example 1. However,the perfluoropolyether having a carboxyl group at one terminal could notbe extracted.

Comparative Example 2 demonstrates a case of the anion-exchange resin asa stationary phase, as described in Japanese Patent ApplicationLaid-Open No. 2012-72272. In Comparative Example 2, the carboxylic acidadsorbed on the anion-exchange resin, so that the perfluoropolyetherhaving a carboxyl group at one terminal was not extracted.

Comparative Example 3

Composition F70 was passed through a 25-millilitre high pressure vesselwhich was filled with silica gel 60 N, ex Kanto Chemical Co., Ltd., in adry particle packing method and a supercritical state carbon dioxide wasused as a moving phase. The pH of the silica gel at 25 degrees C. wasbetween 6.5 and 7.5, and the particle diameter of the silica gel was 40to 100 μm. The flow rate of the moving phase was 15 ml/min and thetemperature was 40 degrees C.

The pressure was 18 MPa, and the temperature and the pressured of themoving phase were not changed, as explained below. First, a fraction wascollected for 10 minutes, then, another fraction was collected for 10minutes and, then, another fraction was collected for 60 minutes. Molarratios of the components in each fraction were as shown in Table 12.

TABLE 12 Amount of a composition Molar ratio of a Pressure, Time, in acompound, % MPa minutes fraction, g (1a) (1b) (1c) 18 10 3.3 27 6 67 1810 3.1 43 7 50 18 60 2.5 65 8 27

As shown in Table 12, when neither the temperature nor pressure of themoving phase changed during the chromatography, any fraction could notcontain the perfluoropolyether having a carboxyl group at one terminalat a higher ratio, i.e. 80 mole % or more.

INDUSTRIAL APPLICABILITY

According to the present method, a composition containing aperfluoropolyether having a carboxyl group at one terminal at a highermolar ratio is efficiently and easily prepared. According to the presentmethod, a composition comprising a perfluoropolyether having afunctional group at one terminal at a high molar ratio can be preparedfrom a perfluoropolyether having functional groups at the bothterminals, even in a case where the perfluoropolyether has a structuresuch that it is difficult to directly introduce a functional group atonly one terminal. Further, the present method can be applied to apolymer having a wide molecular weight distribution. Accordingly, thepresent method is useful for the preparation of starting materials forsurface treatment agents, lubricants and elastomers.

1. A method for increasing a ratio of a perfluoropolyether having acarboxyl group at one terminal, relative to a total amount of theperfluoropolyether having a carboxyl group at one terminal and aperfluoropolyether having carboxyl groups at both terminals in acomposition comprising these perfluoropolyethers, wherein the methodcomprises a step of subjecting the composition to chromatography inwhich a moving phase is a supercritical or subcritical state carbondioxide and a stationary phase is silica gel, and the moving phase is ata constant temperature, T, in a range of from 25 degrees C. to 150degrees C. and a constant pressure, P, in a range of from 7 MPa to 30MPa to thereby collect a fraction containing the perfluoropolyetherhaving a carboxyl group at one terminal at a higher ratio.
 2. The methodaccording to claim 1, wherein the aforesaid chromatography furthercomprises the following step (i) or (ii) after collecting the fractionin the aforesaid process, (i) the pressure of the moving phase isincreased to a constant pressure, P′, which is higher than 7 MPa to 35MPa or lower and is higher than the aforesaid pressure P to therebycollect a fraction containing the perfluoropolyether having carboxylgroups at both terminals at a higher ratio; (ii) the temperature of themoving phase is decreased to a constant temperature, T′, which is 25degrees C. or higher to lower than 100 degrees C. and is lower than theaforesaid temperature T to thereby collect a fraction containing theperfluoropolyether having carboxyl groups at both terminals at a higherratio.
 3. A method for increasing a ratio of a perfluoropolyether havinga carboxyl group at one terminal, relative to a total amount of theperfluoropolyether having a carboxyl group at one terminal, aperfluoropolyether having carboxyl groups at both terminals and aperfluoropolyether having no carboxyl group at any terminal, hereinafterreferred to as a non-functionalized perfluoropolyether, in a compositioncomprising these perfluoropolyethers, wherein the method comprises astep of subjecting the composition to chromatography in which a movingphase is a supercritical or subcritical state carbon dioxide and astationary phase is silica gel and the chromatography comprises thefollowing step (i′) or (ii′): (i′) the moving phase is at a constanttemperature, T₀, of 25 degrees C. or higher to 150 degrees C. or lowerand a constant pressure, P₁, of 7 MPa or higher to lower than 30 MPa tothereby collect a fraction containing the non-functionalizedperfluoropolyether at a higher ratio and, subsequently, the pressure ofthe moving phase is increased to a constant temperature, P₂, which ishigher than 7 MPa to 30 MPa or lower and is higher than the aforesaidpressure P₁ to thereby collect a fraction containing theperfluoropolyether having a carboxyl group at one terminal at a higherratio; (ii′) the moving phase is at a constant temperature, T₁, ofhigher than 25 degrees C. to 150 degrees C. or lower and a constantpressure, P₀, of 7 MPa or higher to 30 MPa or lower to thereby collect afraction containing the non-functionalized perfluoropolyether at ahigher ratio and, subsequently, the temperature of the moving phase isdecreased to a constant temperature, T₂, which is 25 degrees C. orhigher to lower than 150 degrees C. and is lower than the aforesaidtemperature T₁ to thereby collect a fraction containing theperfluoropolyether having a carboxyl group at one terminal at a higherratio.
 4. The method according to claim 3, wherein the aforesaidchromatography further comprises the following step (i″) after aforesaidstep (i′) or the following step (ii″) after aforesaid step (ii′), (i″)the pressure of the moving phase is increased to a constant pressure,P₃, which is higher than 7 MPa to 35 MPa or lower and is higher than theaforesaid pressure P₂ to thereby collect a fraction containing theperfluoropolyether having carboxyl groups at both terminals at a higherratio; (ii″) the temperature of the moving phase is decreased to aconstant temperature, T₃, which is 25 degrees C. or higher to lower than100 degrees C. and is lower than the aforesaid temperature, T₂, tothereby collect a fraction containing the perfluoropolyether havingcarboxyl groups at both terminals at a higher ratio.
 5. The methodaccording to claim 1, wherein the silica gel is such that a waterdispersion containing 10 weight % of the silica gel has pH between 5 and7.5 at 25 degrees C.
 6. A method for preparing a composition comprisingperfluoropolyether having a carboxyl group at one terminal in an amountof 80 mole % or more, relative to a total mole of perfluoropolyethers,wherein the method comprising a step of collecting a fraction containingthe perfluoropolyether having a carboxyl group at one terminal at ahigher ratio according to claim
 1. 7. The method according to claim 6,wherein the composition before subjected to said chromatography is oneprepared by fluorinating a part of carboxyl groups of aperfluoropolyether having carboxyl groups at the both terminals.
 8. Themethod according to claim 6, wherein the composition before subjected tosaid chromatography is one prepared by the following steps: 1) a step offluorinating a part of non-carboxyl functional groups of aperfluoropolyether having the functional groups at the both terminals;and 2) a step of converting the remaining functional group into acarboxyl group.
 9. The method according to claim 8, wherein thefunctional group is an acid fluoride group.
 10. The method according toclaim 6, wherein these perfluoropolyethers have the following structure:—(CF₂)_(d)—(OCF₂)_(p)(OCF₂CF₂)_(q)(OCF₂CF₂CF₂)_(r)(OCF₂CF₂CF₂CF₂)_(s)—O(CF₂)_(d)—wherein d is an integer of from 0 to 5, p and q are, independently ofeach other, an integer of from 5 to 300, r and s are, independently ofeach other, an integer of from 0 to 100, and a total of p, q, r and s is10 to 500, and the parenthesized units may be sequenced at random. 11.The method according to claim 3, wherein the silica gel is such that awater dispersion containing 10 weight % of the silica gel has pH between5 and 7.5 at 25 degrees C.
 12. A method for preparing a compositioncomprising perfluoropolyether having a carboxyl group at one terminal inan amount of 80 mole % or more, relative to a total mole ofperfluoropolyethers, wherein the method comprising a step of collectinga fraction containing the perfluoropolyether having a carboxyl group atone terminal at a higher ratio according to claim 3.